Collmination to be or not to be.

[Gemini2544]

Hi all, as some of you know I'd been having collmination issues. Well Yesterday I nailed the problem & it was not collmination.

The problem was the focal distants from the secondary mirror to the primary mirror. What was happening was I was trying to focus an already out of focus image.

I'm sure you guys have a technical name for this but I don't know it.

Last night I viewed the Orion nebula with the 6.5mm instead of the 30mm for the first time & it was Fantastic...

So. I'll claim last night as FIRST LIGHT.

Thanks for all your help.

Doug :thanx:

[Kevnool]

No collimation issues here.
As you say the views are fantastic.

Cheers Kev.

[shane.mcneil]

Hi Doug,

Glad to hear you have sorted that out. I've been wondering if mine has the same issues. May I ask how you worked out what the distance should be between the two mirrors? And how you set it right?

Regards

Shane

[Gemini2544]

This is trial & error but worth the effort, Wind all three PRIMARY MIRROR screws forward as far as they go. Now wind the screws all the way back counting the turns untill the screws stop.

Now screw them up again but only half as many turns, This puts you at 50% level and it may be right at this point. Now collimate & see a star to confirm. If still out try going up or down in 2 turns at a time or till you discover which direction is improving.

It's a pain but well worth the time to correct.

[floyd_2]

An interesting snippet of info that may help you is to look down the open end of the telescope at the primary and then start walking backwards. At one point the image will flip. This point will be your focal length of the primary (measured from where you were when the image in the primary flipped, to the primary.

Armed with that info, you can measure the distance from the primary to the secondary, and the secondary to the eyepiece. These two distances added should be the same as the focal length you just measured by eyeballing the primary.

Dean

[Gemini2544]

That great to know but how do you get within 1/64" of an inch as required in collmination? Or are you refering to the focal length to calculate your f= number of the apeture? :confused2:

[floyd_2]

I guess I'm off on a bit of a tangent. I'm more getting at a scope that wont come to focus. You need to know your real f/l (vs what may be written on the tube of the scope etc) to see if you're in the ballpark - or which way you need to start adjusting things.

I had similar problems with my second dob a long time back and ended up having to move the primary cell back by about 1/4".

Dean

[Gemini2544]

Thanks Dean I follow you now, I had done the same thing here but without the maths my approch was move it & see. :D